Detecting distance changes

Description

[0001] This invention relates to devices that can detect small changes in distance between opposed surfaces of rollers in imaging devices.

[0002] Imaging devices include, for example, electrophotograhic and electrographic printers, ink jet printers and thermal printers. In these devices, an imaging substrate is fed into a feed path and conveyed through the apparatus to an imaging station for imaging. Multiple imaging substrates, such as paper sheets, are typically stored in stacks in the imaging apparatus. The substrates are separated from each other so that individual substrates are fed into the feed path for imaging.

[0003] A problem that commonly occurs in imaging devices is multifeeds, i.e., multiple substrates that overlie each other being fed into the feed path simultaneously. Multifeeds are caused by adjacent sheets becoming attached. For example, stacks of paper sheets are formed by cutting. When the sheets are cut by a cutting element, edges of adjacent sheets can become attached to each other. If the sheets are not properly separated from each by a separating device of the imaging devices, then two or more sheets can be fed into the feed path as a multifeed. Multifeeds are also caused by electrostatic attraction between adjacent sheets caused by pressure or friction.

[0004] Multifeeds can cause various problems in imaging devices. Imaging devices can image sheets on either one side or on two opposed sides. Imaging devices can include single and tandem print engines for forming one and two-sided images, respectively. When multifeeds occur, sheets can pass through the apparatus without being imaged. In tandem print engine apparatus, when multifeeds occur, it is not possible to print on both opposed sides of a sheet and, thus, two-sided prints can not be formed. In addition, multifeeds can cause jams in the feed paths, requiring imaging to be stopped until the jam can be cleared.

[0005] Multifeeds can also occur in apparatus in which indicia, such as labels, are placed on substrates.

[0006] JP-A-5-301657 describes apparatus for monitoring the passage of sheets comprising a pair of opposed rollers, one of which is fixed and the other of which can move relative to the one roller. A pivoted arm is urged against the movable roller so that it will move correspondingly and a Hall-effect or other magnetic sensor is coupled to the free end of the arm in order to monitor movement of the arm. This is a relatively complex device requiring significant space to accommodate the pivoted arm.

[0007] US-A-5,647,583 describes apparatus for singulating sheets from a stack of sheets including a movable gripper jaw which is pivoted into contact with a sheet to urge the sheet along the surface of a stationary foot. A Hall-effect sensor is provided in the foot in conjunction with a magnet and when the jaw is in the vicinity of the foot, this will be detected by variations in the magnetic field. This arrangement relies on the disturbance of a magnetic field being detected which may be unreliable.

[0008] US-A-5475304 describes a giant magnetoresistant displacement sensor including at least one layered structure. This layered structure includes a harder magnetic (ferromagnetic or antiferromagnetic) layer having a fixed magnetic state, a second, softer, magnetic layer, and a metal layer interposed between and contacting these two layers to prevent exchange coupling between the two layers. The sensor also includes one or more indexing magnets for inducing a domain wall, at a measurand position, between regions of non-aligned magnetic fields in the softer magnetic layer; and an ohmmeter for measuring electrical resistance between points on opposite sides of the structure. In operation, the indexing magnets for inducing a domain wall are positioned relative to the giant magnetoresistant strip. The resistance across the strip is measured, and from this resistance measurement the position of the domain wall is determined. EP 0 548 674 discloses an apparatus for measuring the distance between two rollers, whereby the rollers include permanent magnets and whereby magnetoresistive field sensors are placed at the lateral side of the rollers.

[0009] In accordance with the present invention, we provide a device that detects a change in the distance between opposed surfaces comprising a first roller having a first surface; a second roller having a second surface relatively movable toward or away from the first surface; and magnetic means for monitoring the distance between the first and second surfaces wherein the magnetic means comprises a ferromagnetic material formed as a coating on the second roller, or on a shaft on which the second roller is mounted; and in that the device further comprises a giant magneto resistance effect sensor spaced from the ferromagnetic material, the ferromagnetic material emitting a magnetic field that impinges on the sensor; and a current source that applies a current to operate the sensor, the sensor reading the magnetic field that impinges on the sensor from the ferromagnetic material; wherein the magnetic field emitted by the ferromagnetic material and sensed by the sensor changes when the second surface moves relatively toward or away from the first surface in response to changes in the distance between the first and second surfaces.

[0010] This invention provides devices that can sense small changes in the distance between opposed surfaces of rollers in imaging devices.

[0011] This invention provides in an embodiment apparatus that include the devices. The devices can be retrofitted in the apparatus or can be original components of the apparatus.

[0012] The apparatus may comprise paths for feeding substrates and devices according to this invention for sensing multifeeds of the substrates along the paths.

[0013] The apparatus comprising devices according to this invention are adapted to sense wear and/or contamination of component surfaces that contact substrates.

[0014] The apparatus that comprise devices according to this invention are adapted to sense that improperly sized substrates, such as those having an improper thickness and/or length, have been loaded into the apparatus. The substrates can have various different compositions and can be opaque or light transparent.

[0015] This invention can be used to sense wear or contamination of components in apparatus.

[0016] Under an applied current, the sensor changes it's internal magnetic field coupling and resistivity according to changes in magnitude of the external field that impinges on the sensor from the ferromagnetic material. The magnitude of the external field F between the first and second surfaces is determined by the magnetic properties of the ferromagnetic material; it is also a function of the distance d between the ferromagnetic material's center and a position of interest or location of the sensor. The device senses changes in the distance between the first and second surfaces caused by these surfaces moving relatively toward or away from each other. The changes in the sensor's internal magnetic field and resistivity can be correlated to the change in distance between the first and second surfaces.

[0017] The devices according to this invention can be utilized in various applications in which small distance changes between opposed surfaces indicate a change in some condition or that a problem has occurred. The devices are particularly advantageous for use in an imaging apparatus. The devices can be placed in the feed paths of the imaging apparatus to detect substrate feeding problems, including multifeeds and the feeding of improperly sized substrates. The devices can also be used in imaging apparatus for other purposed, such as to detect wear and/or contamination of surfaces.

[0018] In this invention, applying a current to a giant magneto resistance effect sensor in the presence of an external magnetic field causes the sensor to change it's internal magnetic field coupling and resistivity according to changes in magnitude of the external field that impinges on the sensor from the ferromagnetic material when a first surface moves relatively toward or away from a second surface, such as, for example, when an object passes between the first and second surfaces. The changes in the sensor's internal magnetic field and resistivity are correlated to changes in the distance between the first and second surfaces, which in turn can be correlated to a dimension of the object.

[0019] These and other features and advantages of this invention are described in or are apparent from the following detailed description of various exemplary embodiments of the systems according to this invention.

[0020] Various exemplary embodiments of systems according to this invention will be described in detail, with reference to the following figures, in which:

Fig. 1 illustrates a first exemplary embodiment of a sensing device according to this invention;

Fig. 2 illustrates a second exemplary embodiment of a sensing device according to this invention;

Figs. 3 and 4 are respective top and side views illustrating a first exemplary configuration of a first ferromagnetic material having a cylindrical shape relative to a giant magneto resistance effect sensor;

Figs. 5 and 6 are respective top and side views illustrating a second exemplary configuration of the first ferromagnetic material relative to the giant magneto resistance effect sensor;

Figs. 7 and 8 are respective top and side views illustrating a third exemplary configuration of the first ferromagnetic material relative to the giant magneto resistance effect sensor;

Figs. 9 and 10 are respective top and side views illustrating a first exemplary configuration of a second ferromagnetic material having a rectangular shape relative to the giant magneto resistance effect sensor;

Figs. 11 and 12 are respective top and side views illustrating a second exemplary configuration of the second ferromagnetic material relative to the giant magneto resistance effect sensor;

Fig. 13 is a side view of an exemplary embodiment of a sensing device according to this invention showing the separation between the first and second members during the passage of a single substrate between the members;

Fig. 14 is a side view of the sensing device of Fig. 8 showing the increased separation between the first and second members during the passage of a multifeed, including two substrates, between the members; and

Fig. 15 illustrates an exemplary operation algorithm (not claimed) of the sensing devices according to this invention.

[0021] This invention provides devices that can detect small changes in distance between surfaces, and also apparatus that include the devices. Exemplary embodiments of the devices of this invention can be used in various applications in which changes in distance between surfaces indicate that some condition has changed. For example, a distance change between surfaces can indicate that more than one object, each of the same dimensions, are disposed between the surfaces. A distance change can also indicate that an object is disposed between the surfaces that has a dimension that is either larger or smaller than some nominal value of that dimension. The distance change can also indicate that there has been wear of a member thus changing the distance between that member and another member. The distance change can also indicate that a substance, such as a contaminant, is on a surface of a member, thus changing the apparent distance between that member and another member.

[0022] An exemplary use of the devices according to this invention is in imaging apparatus that comprise paths for conveying substrates for imaging, or for attaching indicia such as labels on the substrates. The devices can be used in these apparatus for various purposes including, for example, sensing multifeeds of the substrates, improper substrate dimensions, wear and/or contamination of components, and other conditions, along the feed paths.

[0023] The devices are particularly advantageous for use in imaging apparatus in which substrates are conveyed along the feed paths to imaging stations to form images on the substrates. Exemplary embodiments of devices according to this invention will be described below with respect to such imaging apparatus.

[0024] In an imaging apparatus, substrates can be imaged on either one side or on two opposed sides. Such an imaging apparatus can include single and tandem print engines for forming one and two-sided images, respectively. During the operation of imaging apparatus, multifeeds can occur due to electrostatic attraction between the sheets, adhesion between the sheets, and other causes. Consequently, jams can occur along the feed paths, requiring the apparatus to be stopped until the jams can be cleared. In addition, when multifeeds occur, substrates can pass through the apparatus without being imaged. In tandem print engine apparatus, when multifeeds occur, it is not possible to print on both of the sides of a substrate and, thus, two-sided prints can not be formed.

[0025] This invention provides devices that can be used in an imaging apparatus to sense the occurrence of multifeeds to reduce feed path jams, to reduce the occurrence of non-imaged substrates, and enhance two-sided print efficiency in a tandem print engine imaging apparatus.

[0026] The devices according to this invention can also be used in an imaging apparatus to sense the wear and/or contamination of surfaces that contact the substrates. Thus, the devices can be used alert operators that the imaging apparatus needs servicing.

[0027] The devices according to this invention can also be used in an imaging apparatus to sense that improperly sized substrates have been loaded into the apparatus for imaging. For example, the devices can be used to sense that the substrates do not have the proper thickness and/or length. Thus, operators can be alerted that different sheets need to be loaded into the apparatus, thus reducing waste.

[0028] Fig. 1 illustrates a device 20 that senses changes in distance between two opposed surfaces according to this invention. The device 20 comprises a first member 30 and a second member 50. The first member 30 comprises a pair of rollers 32, including bearings 34, mounted on a shaft 36. The rollers 32 each have an outer surface 38.

[0029] The second member 50 comprises a roller 52 including a bearing 54 mounted on a shaft 56. In the first exemplary embodiment shown in Fig. 1, a ferromagnetic material 58 is provided on at least a portion of the roller 52. The second member 50 is movably connected to a supporting surface 60 by an elastic element 62, which enables the second member 50 to move relative to the surface 60, as indicated by the arrow 64, such that the second member 50 can move toward or away from the first member 30. The roller configuration shown in Fig. 1 can be, for example, a center register roller configuration, located near the center of the feed path in an imaging apparatus.

[0030] Although the first member 30 is fixed in the exemplary embodiment shown in Fig. 1, the second member 50 can alternatively be fixed while the first member 30 is movable relative to the second member 50. For example, the first member 30 can be connected to a supporting surface using an elastic element, such as the elastic element 62.

[0031] The device 20 comprises a sensor 70 that is positioned to sense an external magnetic field F that impinges on the sensor 70 from the ferromagnetic material 58. The sensor 70 is mounted to the shaft 36 in a manner to allow the shaft 36 to rotate relative to the sensor 70, while the sensor 70 remains stationary.

[0032] Fig. 2 illustrates an embodiment of a device 120 according to this invention. In this second exemplary embodiment, a first member 130 comprises a single roller 132 having a surface 138. A sensor 170 is located next to the roller 132. The sensor 170 senses the external magnetic field F that impinges on the sensor 170 from a ferromagnetic material 158 provided on a second member 150.

[0033] The device 120 can be provided in, for example, an edge register roller configuration, which is typically disposed near the edge of the feed path in an imaging apparatus. This allows for quick service and easy retrofit of the device under any situation. Alternatively, a center register roller configuration, such as that shown in Fig. 1, is placed near the center of the feed path.

[0034] In various exemplary embodiments of the devices 20 and 120 according to this invention, the sensors 70 and 170 are sufficiently sensitive to detect small changes in the distance between opposed surfaces. In the device 20, the sensor 70 can detect changes in the distance between the surfaces 38 and the ferromagnetic material 58. In the device 170 shown in Fig. 2, the sensor 170 can detect changes in the distance between the surface 138 and the ferromagnetic material 158.

[0035] The sensor that has a sufficiently high sensitivity to sense small distance changes is a giant magneto resistance (GMR) effect sensor. In a GMR effect sensor, very thin magnetic and non-magnetic but conductive films are interleaved to produce a magnetic field antiferromagnetically coupled between adjacent magnetic layers, which in turn produces a high resistance (due to electron scattering) when a current is applied to the sensor. When an external field is applied to this arrangement, such as by a ferromagnetic material, the magnetic field between adjacent magnetic layers aligns with the external field in a parallel configuration, decreasing the resistivity of the current flow. A change in the external field due to the movement of the ferromagnetic material with respect to GMR effect sensor, such as caused by changes in the distance between the sensor 70 or 170 and the ferromagnetic material 58 or 158, induces a change in the internal magnetic field coupling and resistivity of the GMR sensor. These changes in resistivity are reflected as linear changes in the voltage output of the sensor. The magnetic field F of a ferromagnetic material is related to the distance d between the sensor and the ferromagnetic material as:

[0036] According to this relationship, even very small changes in d can significantly change, i.e., increase or decrease, the magnetic field F, enabling the sensor 70 or 170 to sense very small distance changes between opposed surfaces.

[0037] The ferromagnetic material 58 or 158 of the devices 20 and 120 can be any suitable ferromagnetic material. For example, the ferromagnetic material 58 and 158 can be a transition metal such as cobalt, nickel or iron; a rare earth element; a metal alloy comprising transition and/or rare earth elements; a ceramic material; a magnetic rubber material, and the like. Exemplary suitable ferromagnetic materials include barium ferrite, strontium ferrite, and aluminum-nickel-cobalt materials.

[0038] The ferromagnetic materials 58 and 158 is formed as a coating on a substrate such as the roller 52 and 152, respectively. The coating can be formed by any suitable coating technique that can apply ferromagnetic materials onto a substrate. The coating can be applied to any suitable substrate material including plastics, metals or ceramics. An exemplary method of coating the substrate comprises forming an electroplated ferromagnetic material layer on a substrate by electroplating.

[0039] In another alternative, the ferromagnetic material 58 can be provided on the shaft 56.

[0040] Alternatively, (not claimed) the ferromagnetic materials 58 and 158 shown in Figs. 1 and 2, respectively, have a ring configuration. The ring of ferromagnetic material 58 or 158 is sized to fit over the rollers 52 or 152, respectively. The ring of ferromagnetic material 58 or 158 can be bonded to the roller 50 or 150 using any suitable bonding technique. The ring of ferromagnetic material 58 or 158 can also be shrink fitted onto the roller 50 or 150. In various The outer surface of the ferromagnetic material 58 and 158 is approximately flush with the outer surface of the roller 52 and 152, respectively, so that the outer surface of the roller 52 and 152 makes proper contact with substrates that pass between the first member 30 or 130 and the second member 50 or 150 during imaging.

[0041] The sensors 70 and 170 can be mounted at any suitable location of the first member 30 and 130, respectively. For example, the sensor 70 can be mounted on the shaft 36 between the rollers 32, as shown in Fig. 1, or on the shaft 136 adjacent to the roller 132, as shown in Fig. 2.

[0042] However, in other exemplary embodiments, the sensor can alternatively be mounted to some other member in the apparatus in which the device is installed.

[0043] In still other exemplary embodiments of the devices of this invention, the position of the ferromagnetic material can be varied with respect to the sensor. Figs. 3-12 show different exemplary configurations of ferromagnetic materials relative to a fixed sensor. Figs. 3 and 4, 5 and 6, and 7 and 8, respectively, show respective top and side views of three different configurations of a cylindrical shaped ferromagnetic material 258 relative to a sensor 270. As shown, the position of the ferromagnetic material 258 along the y-axis corresponding to the longitudinal axis of the sensor 270 is varied. In the configuration shown in Figs. 3 and 4, the ferromagnetic material 258 is approximately centrally located along the length of the sensor 270. In Figs. 5 and 6, the ferromagnetic material 258 is located along the y-axis near an edge of the sensor 270. In Figs. 7 and 8, the ferromagnetic material 258 is located along the y-axis near outward from the edge of the sensor 270, such that surfaces of the ferromagnetic material 258 and the sensor 270 do not directly overlie and face each other.

[0044] Figs. 9 and 10, and 11 and 12, respectively, each show respective top and side views of two different configurations of a rectangular shaped ferromagnetic material 358 relative to a sensor 370. In Figs. 9 and 10, the ferromagnetic material 358 is oriented parallel to, and offset in the x-axis direction from, the sensor 370. In Figs. 11 and 12, the ferromagnetic material 358 is oriented vertically along the z-axis, approximately above the center of the sensor 370 along the y-axis.

[0045] In tests conducted by the inventors of this invention, two giant magneto resistance (GMR) effect sensors having different sensitivities were used in combination with the ferromagnetic material configurations shown in Figs. 3-12. The giant magneto resistance (GMR) effect sensors 270 and 370 were Model Nos. AA005-02 and AA002-02 manufactured by NVE Inc. of Eden Prarie, Minnesota, having respective sensitivities of 0.45-0.65 mV/V/Oe and 3-4.2 mV/V/Oe. The ferromagnetic material 258 shown in Figs. 3-8 had a composition of barium-ferrite and strontium-ferrite. The ferromagnetic material 358 shown in Figs. 9-12 had a composition of aluminum-nickel-cobalt.

[0046] The test results indicated that the configuration shown in Figs. 7 and 8 provided the largest range of movement of the ferromagnetic material 258 in the z-axis direction (about 2.7 mm) over which the response sensitivity of the giant magneto resistance effect sensor 270 was above a desired value of about 220mV/mm. The increased range provides increased adjustabilty in the placement of the ferromagnetic material 258 and the sensor 370. The increased range also allows distance changes to be sensed for objects such as substrates having increased thickness. The configuration shown in Figs. 5 and 6 provided a range of movement of the ferromagnetic material 258 in the z-axis of about 2.1 mm.

[0047] For the rectangular ferromagnetic material 358 shown in Figs. 9-12, the configuration shown in Figs. 11 and 12 provided the highest range of movement of the ferromagnetic material 358 in the z-axis direction. This range is about 1.6 mm over which the response sensitivity of the giant magneto resistance effect sensor 370 was above about 220mV/mm.

[0048] It will be understood by those skilled in the art that the configurations shown in Figs. 3-12 are exemplary only. Other suitable configurations of the ferromagnetic material and the giant magneto resistance effect sensor can also be used, in which any changes on the external magnetic field from the ferromagnetic material will make the internal magnetic field coupling of the sensor realign with it in a parallel manner, changing the sensor's resistivity and voltage output accordingly.

[0049] In various exemplary embodiments of the devices according to this invention, the devices can detect changes in distance between surfaces as small as about 0.01 mm leading to sensor outputs around 2000 mV/mm. This thickness is ten times less than the thickness of sheets, such as Xerox 4020-20# paper, typically used in imaging apparatus. These sheets typically have a thickness of about 0.1 mm. Thus, the devices are sufficiently sensitive to sense multifeeds of paper in imaging apparatus.

[0050] An exemplary embodiment of a method of sensing distance changes between surfaces will be described with reference to Figs. 13 and 14. Fig. 13 shows a single substrate 400 passing between an upper roller 452 comprising a ferromagnetic material 458 forming at least a surface region 460 of the upper roller 452, and a lower roller 432. The substrate 400 can comprise paper, cardboard, plastic or some other material. Typically, the upper roller 452 and the lower roller 432 contact each other when the substrate 400 is not located between them. The upper roller 452 and/or the lower roller 432 can be resiliently biased so that the substrate 400 causes the upper roller 452 and the lower roller 432 to be separated from each other when the substrate 400 passes between them.

[0051] A sensor 470, a giant magneto resistance (GMR) effect sensor, is positioned to sense a magnetic field F₁ that can pass through the substrate 400 from the ferromagnetic material 458 located on the opposite side of the substrate 400. When a single substrate 400 passes between the upper roller 452 and the lower roller 432, the magnetic field F₁ has a value that can be correlated to the distance between the upper roller 452 and the lower roller 432. Because this distance corresponds to the thickness x of the substrate, the magnetic field F₁ can be correlated with the substrate thickness.

[0052] Fig. 14 shows a multifeed where two of the substrates 400 pass between the upper roller 452 and the lower roller 432. The multifeed causes the distance between the upper roller 452 and the lower roller 432 to be increased to a distance 2x, which equals the total thickness of the two substrates 400. The magnetic field F₂ read by the sensor 470 is consequently decreased to a value equal to 1/8 F₁. Thus, the sensor 470 has sufficient sensitivity to enable the occurrence of multifeeds to be readily sensed.

[0053] As described above in accordance with the various exemplary embodiments of this invention, the devices can be used to sense that improper substrates have been loaded into an apparatus. For example, referring to Fig. 13, when the substrate 400 having a thickness x is disposed between the upper roller 452 and the lower roller 432, the magnetic field F read by the sensor from the ferromagnetic material equals F₁. If a single substrate 400 having a thickness that differs from x is passed between the upper roller 452 and the lower roller 432, the magnetic field F increases or decreases, depending on whether the substrate 400 thickness is greater or less than x. If the thickness of the substrate 400 exceeds x and equals x + Δx, then the magnetic field emitted by the sensor 470 decreases to a value F_{x + Δx}, which is less than F₁. If the thickness of the substrate 400 is less than x and equals x - Δx, then the magnetic field emitted by the sensor 470 is increased to a value F_{x - Δx}, which is greater than F₁.

[0054] Because the resistivity and internal magnetic coupling of giant magneto resistance (GMR) effect sensors is extremely sensitive to the separation between the sensor 470 and a ferromagnetic material 458, the sensors can detect very small differences in thickness Δx of the substrates. As stated above, giant magneto resistance (GMR) effect sensors can detect changes in distance between surfaces as small as about 0.01 mm. This distance is about 10% of the thickness of a typical sheet of paper used in imaging apparatus. Thus, these sensors can sense an improper sheet thickness of sheets that varies by as little as about 10% from a typical sheet thickness.

[0055] As stated above, other exemplary embodiments of the devices according to this invention can also be used to sense improper object lengths. Referring to Fig. 13, the object 400 has a length L. Accordingly, the entire object can pass between the rollers in an amount of time t given by: t = L/f, where f is the feed rate (distance/time) of the object 400 between the upper roller 452 and the lower roller 432. Thus, when the object 400 of length L passes between the rollers at the feed rate f, the magnetic field read by the sensor 470 has a value F for the amount of time t. After the object has passed through the upper roller 452 and the lower roller 432, the upper roller 452 and lower roller 432 move toward each other and the magnetic field changes due to the decrease in separation between them.

[0056] If an object 400 of the same thickness, but having a length either longer or shorter than L, passes between the upper roller 452 and the lower roller 432, then the magnetic field F corresponding to the thickness of that object 400 will be read for an amount of time greater than t, when the object length exceeds L, or for an amount of time less than t, when the object length is less than L. The devices according to this invention accordingly allow improper object lengths to be sensed by comparing the amount of time that the magnetic field of the value F is read to a predetermined amount of time that corresponds to an object having the desired length L.

[0057] As stated above, various exemplary embodiments of the devices according to this invention can also be used to sense the wear of component surfaces. Referring to Fig. 13, the upper roller 452 has an outer diameter of D. As the outer surface 460 of the upper roller 452 wears, the outer diameter of the upper roller 452 decreases by an amount ΔD. This decrease in the outer diameter of the upper roller 452 decreases the distance between the outer surface 460 of the upper roller 452 and the sensor 470. Thus, the magnetic field F read by the sensor 470 increases. Accordingly, the device 420 can sense wear of the upper roller 452 based on this change in the magnetic field when the wear causes a change in the outer diameter of the upper roller 452 that is within the sensitivity of the sensor 470.

[0058] As stated above, various exemplary embodiments of devices according to this invention can also be used to sense the presence of contaminants on component surfaces. Referring to Fig. 13, if contaminants are present on the outer surface 460 of the upper roller 452, the distance between the outer surface 460 and the sensor 452 increases by an amount equal to about the depth of the contaminants on the outer surface 460. Consequently, the magnetic field F read by the sensor 470 decreases. Accordingly, if the contaminant depth is within the sensitivity of the sensor 470, then by comparing the magnetic field read by the sensor 470 in a clean condition of the outer surface 460 of the upper roller 452, to the magnetic field read by the sensor 470 after operation of the device 420, the presence of contamination on components, such as rollers in an imaging apparatus, can be sensed.

[0059] Even though wear and contaminants can be measured by the sensor 470, this will not affect the ability of the sensor 470 to detect multifeeds if a proper algorithm is implemented. Referring to Fig.15, the sensor 470 gives a voltage output porportional to the substrate thickness. When no substrate is present, the output voltage is v₀. When a substrate is present, the output voltage is v_n. The actual substrate thickness V_N is:

[0060] Some exemplary cases are:

a) If V_N > (V_T = X·V_N-1), where X is a factor larger than one determined from testing, then there is a multifeed.

b) At any time t, if wear of a component has occurred, the distance between the sensor and the ferromagnetic material has decreased, increasing the magnetic field F and the output voltage of the sensor. Then, v₀ depends on t and v₀(t) > v₀(0).

c) At any time t, if contamination has occurred, the distance between the sensor and the ferromagnetic material has increased, decreasing the magnetic field F and the output voltage of the sensor. Then, v₀ depends on t and v₀(t) < v₀(0).

[0061] Based on cases (b) and (c), when wear or contamination, the value of v₀ changes. From the exemplary configuration shown in Figs. 7 and 8, v₀ can have values corresponding to a Z position of z = 3.7 to 6.4 mm (Δz = 2.7 mm) and still give a multifeed output of at least 220 mV/mm. Accordingly, contamination and/or wear can occur without affecting the multifeed detection performance of the devices according to this invention.

[0062] The devices according to this invention can be used to detect multifeeds and improper substrate sizes for various substrate materials in an imaging apparatus. For example, the imaging substrates can comprise various types of paper, cardboard and the like. The substrates can also comprise light transparent materials, such as polymeric materials used to form transparencies. The devices according to this invention provide the advantage that it is not necessary to place a detecting strip on light transparent materials, as in conventional systems that include optical sensors, to be able to detect these materials.

[0063] The substrates can be sheets as well as envelopes and like. The substrates can have various dimensions and shapes.

[0064] It is contemplated that the devices can also be used in apparatus that feed metallic substrates, such as thin metallic sheets. In those embodiments, the giant magneto resistance effect sensor and the ferromagnetic material should be positioned so that the magnetic field emitted by the ferromagnetic material and read by the sensor is not adversely affected by the thin metallic sheet. In addition, composite materials can also be sensed with the devices.

Claims

1. A device adapted for detecting a change in the distance between opposed surfaces, comprising:

a first roller (32) having a first surface (38);

a second roller (52) having a second surface relatively movable toward or away from the first surface; and

magnetic means for monitoring the distance between the first and second surfaces, wherein the magnetic means comprises a ferromagnetic material (58) formed as a coating on the second roller (52), or on a shaft on which the second roller is mounted; and in that the device further comprises a giant magneto resistance effect sensor operatively associated with the first surface, and (70) spaced from the ferromagnetic material (58), the ferromagnetic material emitting a magnetic field that impinges on the sensor; and

a current source that applies a current to operate the sensor (70), the sensor reading the magnetic field that impinges on the sensor from the ferromagnetic material;

wherein the magnetic field emitted by the ferromagnetic material (58) and

sensed by the sensor changes when the second surface moves relatively toward or away from the first surface in response to changes in the distance between the first and second surfaces.

2. A device according to claim 1, wherein the second surface comprises the ferromagnetic material (158).

3. A device according to claim 1 or 2, wherein the second surface is movable with respect to the first surface when an object passes between, and contacts, the first and second surfaces.

4. A device according to claim 3, wherein the object is light transparent.

5. A device according to claim 3 or 4, wherein the object comprises at least one sheet.

6. A device according to any one of the preceding claims, wherein the first surface and the second surface do not directly face each other.

7. An apparatus, comprising:

a feed path for conveying objects through the apparatus; and

a device that detects changes in the distance between opposed surfaces according to any one of the preceding claims defining a portion of the feed path.

Ansprüche

1. Vorrichtung, die so eingerichtet ist, dass sie eine Änderung des Abstandes zwischen einander gegenüberliegenden Flächen erfasst, wobei sie umfasst:

eine erste Rolle (32) mit einer ersten Fläche (38);

eine zweite Rolle (52) mit einer zweiten Fläche, die relativ zu der ersten Fläche auf sie zu oder von ihr weg bewegt werden kann; und

eine magnetische Einrichtung zum Überwachen des Abstandes zwischen der ersten und der zweiten Fläche, wobei die magnetische Einrichtung ein ferromagnetisches Material (58) umfasst, das als eine Beschichtung auf der zweiten Rolle (52) oder auf einer Welle ausgebildet ist, an der die zweite Rolle angebracht ist, und die Vorrichtung des Weiteren einen GMR-Effekt-Sensor (70) umfasst, der funktional mit der ersten Fläche verbunden ist und von dem ferromagnetischen Material (58) beabstandet ist, wobei das ferromagnetische Material ein Magnetfeld emittiert, das auf den Sensor auftrifft; und

eine Stromquelle, die einen Strom zum Betreiben des Sensors (70) anlegt, wobei der Sensor das Magnetfeld misst, das auf den Sensor von dem ferromagnetischen Material auftrifft;

und sich das von dem ferromagnetischen Material (58) emittierte und durch den Sensor erfasste Magnetfeld ändert, wenn sich die zweite Fläche in Reaktion auf Änderungen des Abstandes zwischen der ersten und der zweiten Fläche relativ zu der ersten Fläche auf sie zu oder von ihr weg bewegt.

2. Vorrichtung nach Anspruch 1, wobei die zweite Fläche das ferromagnetischen Material (158) umfasst.

3. Vorrichtung nach Anspruch 1 oder 2, wobei die zweite Fläche in Bezug auf die erste Fläche bewegt werden kann, wenn ein Objekt zwischen der ersten und der zweiten Fläche hindurchtritt und mit ihnen in Kontakt kommt.

4. Vorrichtung nach Anspruch 3, wobei das Objekt lichtdurchlässig ist.

5. Vorrichtung nach Anspruch 3 oder 4, wobei das Objekt wenigstens ein Blatt umfasst.

6. Vorrichtung nach einem der vorangehenden Ansprüche, wobei die erste Fläche und die zweite Fläche einander nicht direkt zugewandt sind.

7. Vorrichtung, die umfasst:

einen Zuführweg zum Transportieren von Objekten durch die Vorrichtung; und

eine Einrichtung nach einem der vorangehenden Ansprüche, die Änderungen des Abstandes zwischen einander gegenüberliegenden Flächen erfasst und die einen Abschnitt des Zuführweges bildet.

Revendications

1. Dispositif adapté pour détecter un changement dans la distance entre des surfaces opposées, comprenant :

un premier rouleau (32) ayant une première surface (38) ;

un deuxième rouleau (52) ayant une deuxième surface relativement mobile vers la première surface ou loin de celle-ci ; et

un moyen magnétique permettant de surveiller la distance entre les première et deuxième surfaces, dans lequel le moyen magnétique comprend un matériau ferromagnétique (58) formé sur un revêtement sur le deuxième rouleau (52), ou sur un arbre sur lequel est monté le deuxième rouleau ; et en ce que le dispositif comprend en outre un capteur (70) à effet magnéto-résistif géant associé de manière fonctionnelle à la première surface, et espacé du matériau ferromagnétique (58), le matériau ferromagnétique émettant un champ magnétique qui s'imprègne sur le capteur ; et

une source de courant qui applique un courant pour faire fonctionner le capteur (70), le capteur lisant le champ magnétique qui s'imprègne sur le capteur depuis le matériau ferromagnétique ;

dans lequel le champ magnétique émis par le matériau ferromagnétique (58) et détecté par le capteur change lorsque la deuxième surface se déplace relativement vers la première surface ou loin de celle-ci en réponse à des changements dans la distance entre les première et deuxième surfaces.

2. Dispositif selon la revendication 1, dans lequel la deuxième surface comprend le matériau ferromagnétique (158).

3. Dispositif selon la revendication 1 ou 2, dans lequel la deuxième surface est mobile par rapport à la première surface lorsqu'un objet passe entre les première et deuxième surfaces et vient en contact avec celles-ci.

4. Dispositif selon la revendication 3, dans lequel l'objet est une lumière transparente.

5. Dispositif selon la revendication 3 ou 4, dans lequel l'objet comprend au moins une feuille.

6. Dispositif selon l'une quelconque des revendications précédentes, dans lequel la première surface et la deuxième surface ne se font pas directement face.

7. Appareil, comprenant :

un chemin d'alimentation pour acheminer des objets à travers l'appareil ; et

un dispositif qui détecte des changements dans la distance entre des surfaces opposées selon l'une quelconque des revendications précédentes définissant une partie du chemin d'alimentation.

Drawing